(a continuation) #11. James Polk With the border region of Mexico and the United States in dispute, James Polk initially set out to achieve diplomatic reconciliation. But when Mexico declined his initial buy-out offer, Polk deemed Mexican presence in this disputed region enough to declare war. Over time, U.S. military strength caused Mexico to concede and accept financial terms less than originally offered. While this resulted in a substantial increase of American land, it also enraged a neighboring country where resentment of this action still lingers today.